The present invention relates to picture quality improving apparatus applicable to various video devices and apparatus such as television (TV) image receiving apparatus, video tape recorders (VTR) and the like, and various image processing apparatus handling image data and the like. More particularly, the present invention relates to picture quality improving apparatus applicable to digital circuits and capable of improving a distinction and a resolution of represented images by means of an improvement of a color blur phenomenon. The improvement is performed by stressing an envelope edge of a chrominance signal whose amplitude is modulated such that a person watching a picture feels an intact picture without a sense of incongruity.
There has been conventionally performed contour compensation used for improving a picture quality in which a contour compensation component is obtained by a quadratic differential calculation to add the proper quantity of the component to an original signal. In contour compensation by the above method, a quadratic differential waveform as a contour compensation component has a peak which is considerably outside a midpoint of a change portion (edge portion) of a waveform of the original signal. Accordingly, when the quadratic differential waveform is added to the original signal, it is possible to generate a preshoot and an overshoot so as not to obtain a picture improving effect at a desired degree. Furthermore, it is possible to perform artificial contour compensation in that an edging of other colors such as white and black occurs at edges of the reproduced picture.